JP5898081B2 - X-ray CT system - Google Patents

Description

The present invention relates to an X-ray CT apparatus that obtains an X-ray CT image by irradiating a subject with X-rays, and particularly relates to a technique for measuring an irradiation dose to a subject and an exposure dose of the subject.

  The International Commission on Radiological Protection (ICRP) recommended in 2007 that `` Protect humans and the environment at an appropriate level from the harmful effects of radiation exposure without overly restricting activities involving radiation exposure. '' Yes. This ICRP recommendation is recommended for medical X-ray exposure in diagnostic imaging.

  For application to medical X-ray exposure, it is necessary to measure the X-ray exposure dose. In Patent Document 1, information related to an exposure dose when a predetermined amount of X-rays are irradiated for a predetermined time is stored in a storage unit, and each part of the subject corresponding to each position in a reconstructed X-ray tomogram is stored. The approximate constant X-ray dose reached is calculated by the X-ray dose calculation unit, and based on the information on the exposure dose, the calculated X-ray dose reaching each part, and the X-ray irradiation time, Since the exposure dose distribution of the subject by the X-rays irradiated when reconstructing the line tomographic image is calculated by the exposure dose distribution calculation unit, the exposure dose distribution for each part of the subject is calculated.

Japanese Unexamined Patent Publication No. 2005-74000

However, in Patent Document 1, since the dose is calculated based on an approximate constant dose, the more the number of regions having different CT values in the CT tomographic image, such as organs and tissues, the more the dose is calculated. This calculation amount increases.
Therefore, there is still a problem to be solved that the calculation processing time for calculating the exposure dose becomes longer and it takes time to evaluate the exposure dose of the subject.
An object of the present invention is to provide an X-ray CT apparatus capable of quickly evaluating the exposure dose of a subject.

  In order to achieve the above object, the present invention acquires an irradiation X-ray image that is a distribution of irradiation intensity of X-rays irradiated to a subject by an X-ray irradiation unit according to imaging conditions, and the irradiation X-rays The image and the reconstructed image are projected and converted, and the projected reconstructed image and the irradiation X-ray image corresponding to the reconstructed image creation region are used to indicate the exposure dose distribution of the subject. An image reconstruction unit that creates an exposure dose image and calculates the exposure dose is provided.

  According to the present invention, the exposure dose of a subject can be quickly evaluated.

Diagram showing the overall configuration of the X-ray CT system Diagram showing components of X-ray CT system Flowchart showing the flow of dose evaluation processing in the first embodiment The figure explaining the irradiation dose image creation processing in 1st Embodiment The flowchart which shows the flow of the exposure dose image creation process in 1st Embodiment The figure explaining the exposure dose image creation process in 1st Embodiment The figure which shows an example of the screen which displays dose evaluation information The figure explaining the irradiation dose image creation processing in 2nd Embodiment The flowchart which shows the flow of the exposure dose image creation process in 2nd Embodiment The figure explaining the exposure dose image creation process in 2nd Embodiment The figure explaining the cumulative irradiation dose image creation process in 3rd Embodiment The figure explaining the accumulated exposure dose image creation process in 4th Embodiment

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The present invention evaluates an exposure dose in an image diagnosis performed using an X-ray CT apparatus.

[First embodiment]
First, the configuration of the X-ray CT apparatus according to the present invention will be described with reference to FIG. 1 and FIG.
As shown in FIG. 1, the X-ray CT apparatus includes an imaging unit 1, an operation unit 2, and the like. The photographing means 1 includes a gantry 100 that houses a scanner main body and a bed apparatus 101. The operating means 2 operates and controls the photographing means 1. The operation means 2 performs input of shooting conditions, image processing, and the like.

As shown in FIG. 2, the gantry 100 includes an X-ray generator 102 that irradiates X-rays from around the subject 3, a collimator device 104 that narrows the X-ray beam bundle generated from the X-ray generator 102, and the subject. X-ray detection device 103 for detecting X-rays transmitted through 3, high-voltage generation device 105 for applying a high voltage to the X-ray generation device 102, data collection device 106 for collecting data detected by the X-ray detection device 103, scanner Is composed of a drive device 107 and the like that rotate the patient 3 around the subject 3. The collimator device 104 may include a compensation filter for adjusting the X-ray irradiation distribution.

The operation means 2 includes an input / output device 201, a calculation device 202, a central control device 200, and the like.
The input / output device 201 includes a display device 211 that displays data such as images, an input device 212 for an operator to input shooting conditions, a storage device 213 that stores data necessary for shooting such as programs and device parameters, and the like. Consists of

  The arithmetic device 202 includes an image reconstruction device 221 that creates a reconstructed image or the like of the subject 3 based on data obtained from the imaging means 1, an image processing device 222 that analyzes image data, and the like. The central control device 200 controls each of the photographing unit 1 and the operation unit 2 in accordance with an operation instruction from the operator.

  Imaging with the X-ray CT apparatus is a rotating imaging in which the X-ray generator 102 and the data collection device 106 rotate while taking the image in the gantry 100, and the X-ray generation device 102 and the data collection device 106 are stationary in the gantry 100. There is still shooting for shooting. Tomographic imaging for obtaining a tomographic image of the subject 3 is based on rotational imaging. Scanogram imaging for determining the tomographic imaging position is based on still imaging. The tomographic imaging trajectory may be any of a circular trajectory, a spiral trajectory, a combination of a circular trajectory and a spiral trajectory, and is not particularly limited.

Here, the X-ray CT apparatus composed of the imaging means 1 and the operation means 2 shown in FIGS. 1 and 2 is connected to each other such as a display device and an input / output device provided in the X-ray CT apparatus by a wiring or network. It can be understood as an X-ray CT device that is electrically connected by, for example. Furthermore, if the data processing apparatus, such as a workstation or a desktop computer, as shown in the operating means 2 in FIG. 1, such devices are replaced as follows. That is, the input / output device 201 constituting the operation means 2 is an input / output unit, the central control device 200 is a control unit, and the calculation device 202 is a calculation unit. With such a configuration, such a data processing device is the same as that of an integrated stand-alone type device.

Similarly, in the imaging means 1 of FIG. 1, the X-ray generator 102 is an X-ray generator, the collimator device 104 is a collimator unit, and the X-ray generator and the collimator unit are configured. The X-ray detection device 103 is an X-ray detection unit, the high voltage generation device 105 is a high voltage generation unit, the data collection device 106 is a data collection unit, and the drive device 107 is a drive unit. That is, the photographing means 1 includes these parts, the gantry 100, and the bed apparatus 101. Each part of the imaging means 1 and the operating means 2 has the same function as the above-described apparatus.
Furthermore, the “X-ray irradiation unit”, “X-ray detection unit”, “image reconstruction unit”, and “display unit” are defined as follows.

  The “X-ray irradiation unit” irradiates X-rays from around the subject. The X-ray generation unit 102 irradiates X-rays from around the subject 3 and the X-ray generation unit 102 generates X-rays. And a collimator unit 104 for narrowing a bundle of lines.

  The “X-ray detection unit” detects X-rays transmitted through the subject as X-ray information, and corresponds to the X-ray detection device 103.

  The “image reconstruction unit” creates a reconstructed image of the subject from the X-ray information detected by the X-ray detection unit. Acquire an irradiation X-ray image that is the distribution of the irradiation intensity of the irradiated X-ray, project the irradiation X-ray image and the reconstructed image, and correspond to the reconstructed image and the reconstructed image creation area The image reconstruction device 221 corresponds to an exposure dose image that is an image showing the distribution of the exposure dose of the subject using the irradiated X-ray image, and calculates the exposure dose.

The “display unit” displays an exposure dose image and an exposure dose, and corresponds to the display device 211.
In the present embodiment, the image reconstruction unit (image reconstruction device 221) evaluates the exposure dose of the subject 3 by executing a process flow to be described later.

Here, definitions of terms are described.
The “image” is not limited to what is visually displayed on the display device, but also means pixel value aggregate data. Then, “creating an image” means calculating each pixel value.
In addition, if the X-ray dose (irradiation dose) irradiated to the subject 3 and the X-ray dose (exposure dose) indicating the exposure dose of the subject 3 are not distinguished, they are simply described as “dose”. I decided to.
“Irradiated X-ray information” is a distribution of irradiation intensity of X-rays irradiated to the subject 3 by the X-ray generator 102.
The “irradiation X-ray image” and “irradiation dose image” are images showing the distribution of the X-ray irradiation dose irradiated to the subject 3.

An “attenuation coefficient image” is an image showing the distribution of attenuation coefficients.
The “irradiation dose correction image” is an image showing a reduction result of the attenuation amount with respect to the irradiation dose image. That is, the irradiation dose correction image is an image showing the result of reducing the attenuation by the subject 3 from the irradiation dose image.

  The “absorbed dose image” is an image showing the distribution of X-ray absorbed dose absorbed by the subject 3. Absorbed dose is the basic dosimetric measure in radiation protection and is defined as the energy absorbed per unit mass. The unit of absorbed dose is J / kg (special unit is Gy (gray)).

  An “equivalent dose image” is an image showing the distribution of equivalent dose. The equivalent dose is the product of the average absorbed dose in each organ or tissue and the radiation weighting factor. The unit of equivalent dose is J / kg (special unit is Sv (sievert)). According to the ICRP recommendation, the radiation weighting factor for photons is 1, not limited to the energy range, so the absorbed dose is equivalent to the equivalent dose in CT.

  An “effective dose image” is an image showing an effective dose. Effective doses are weighted by the International Commission on Radiological Protection (ICRP) by weighting the tissue weighting factors that represent different radiation sensitivities for organs and / or tissues (hereinafter referred to as organs) with respect to equivalent doses. It is defined as the total value of etc. The unit of effective dose is J / kg (special unit is Sv (sievert)).

The “organ discrimination image” is an image for identifying a region such as an organ included in the reconstructed image.
A “tissue load coefficient image” is an image obtained by weighting an equivalent dose image with a tissue load coefficient for each region such as an organ identified by an organ discrimination image.

  The “exposure dose image” is an image showing the distribution of the exposure dose of the subject 3. The exposure dose image is calculated as an effective dose image, for example.

Next, processing of the X-ray CT apparatus in the first embodiment will be described with reference to FIGS.
As shown in FIG. 3, the image reconstruction device 221 of the X-ray CT apparatus acquires a subject image (S101).
The subject image in the first embodiment is a tomographic image 5 (reconstructed image) of the subject 3 shown in FIG. A tomographic plane of the tomographic image 5 is a region 4a indicated by a dotted line. The tomographic image 5 may be either a single image or a plurality of images, and is not particularly limited. Further, the subject image in the first embodiment is not only a cross-sectional image (axial image) perpendicular to the body axis of the subject 3 as in the tomographic image 5, but also the body axis of the subject 3. A cross-sectional image (coronal image) parallel to the side of the subject 3 and a cross-sectional image parallel to the body axis of the subject 3 and from the front to the back of the subject 3 (sagittal image), etc. Also good.

Next, the image reconstruction device 221 of the X-ray CT apparatus acquires irradiation X-ray information from the storage device 213 according to the imaging conditions (S102).
The image reconstruction device 221 performs irradiation X-rays at each time (t = t0,..., Tn) at predetermined time intervals from the start of X-ray irradiation (t = t0) to the end of irradiation (t = tn). Information is acquired from the storage device 213. In other words, the image reconstruction device 221 acquires irradiation X-ray information corresponding to the imaging conditions at predetermined time intervals (for example, for each view).

  The irradiation X-ray information is the three-dimensional irradiation intensity distribution data 1001 shown in FIG. The image reconstruction device 221 stores the three-dimensional irradiation intensity distribution data 1001 in the storage device 213 for each imaging condition before S102.

  In the example shown in FIG. 4, the three-dimensional irradiation intensity distribution data 1001 includes the X-ray beam spread (fan angle) in the slice plane direction (xy plane direction) and the X-ray beam in the body axis direction (z axis direction). Of spread (cone angle). However, the three-dimensional irradiation intensity distribution data 1001 is not limited to the example shown in FIG.

  The three-dimensional irradiation intensity distribution data 1001 may be any of data measured in advance before capturing the tomographic image 5, data obtained during capturing of the tomographic image 5, or data obtained by numerical simulation. The three-dimensional irradiation intensity distribution data 1001 may be data obtained by modeling or parameterizing actual measurement data or simulation data.

  The three-dimensional irradiation intensity distribution data 1001 varies depending on the voltage and current (tube voltage, tube current) applied to the X-ray generator 102. Further, it varies depending on the degree of opening of the collimator portion of the collimator device 104. It also depends on the geometric characteristics of the gantry 100. The three-dimensional irradiation intensity distribution data 1001 is not particularly limited to imaging conditions, and can be defined according to various imaging conditions.

Returning to the description of FIG. Next, the image reconstruction device 221 of the X-ray CT apparatus creates an irradiation dose image (S103).
The image reconstruction device 221 creates three-dimensional irradiation dose data 2000 by time-integrating a set 1000 of a plurality of three-dimensional irradiation intensity distribution data acquired in S102. The three-dimensional irradiation dose data 2000 is a total sum of X-ray doses irradiated from the start of X-ray irradiation (t = t0) to the end of irradiation (t = tn). Then, the image reconstruction device 221 uses a region 4b having the same z position as the region 4a indicating the tomographic plane of the tomographic image 5 as the cutout plane, and uses the three-dimensional irradiation dose data 2000 on the cutout plane. These pixel values are extracted as an irradiation dose image 6.

  Note that the irradiation dose image 6 shown in FIG. 4 is expressed so that the pixel values of the circular region are constant, but actually have different pixel values for each pixel. That is, the irradiation dose image 6 is an image having a distribution.

As shown in FIG. 4, the region of the three-dimensional irradiation dose data 2000 has, for example, an inner peripheral surface of the gantry 100 (an opening of the gantry 100) as a cross section, and X-rays reach the body axis direction (z-axis direction). A cylindrical shape that extends from the minimum Z position to the maximum Z position (determined by the shooting start position and the shooting end position, respectively). However, the shape of the region of the three-dimensional irradiation dose data 2000 is not limited to this, and may include at least an X-ray irradiation range that may be irradiated to the subject 3 at the time of imaging. For example, the cross section of the region of the three-dimensional irradiation dose data 2000 is not limited to a circle but may be an ellipse or a rectangle. Moreover, the cross section of the region of the three-dimensional irradiation dose data 2000 may have different areas in the body axis direction (z-axis direction).
Returning to the description of FIG. Next, the image reconstruction device 221 of the X-ray CT apparatus creates an exposure dose image (S104).

The exposure dose image creation process will be described below with reference to FIGS.
As shown in FIG. 5, the image reconstruction device 221 acquires the tomographic image 5 shown in FIG. 4 (S201), and based on the information indicating the relationship between the CT value and the linear attenuation coefficient, the attenuation coefficient image from the tomographic image 5 Conversion to 7 (S202).

  The relationship between the CT value and the linear attenuation coefficient is “CT value = (μt−μw) / μw × K” (μt: subject 3 linear attenuation coefficient, μw: water linear attenuation coefficient, K: constant) It is expressed by a relational expression.

  The linear attenuation coefficient is a physical coefficient determined by the energy distribution of the irradiated X-rays and the substance constituting the subject 3. Information indicating the relationship between the CT value and the attenuation coefficient (conversion data for converting the CT value into the attenuation coefficient) depends on imaging conditions, characteristics of the X-ray CT apparatus, and the like. The conversion data may be data measured in advance before the tomographic image 5 is taken, data obtained by numerical simulation, or data obtained by modeling or parameterizing the measured data or simulation data.

  Next, the image reconstruction device 221 performs forward projection (also referred to as reprojection) processing on the attenuation coefficient image 7 and converts it into attenuation coefficient projection data 50 (S203). Here, the forward projection process is a process of converting the distribution of the linear attenuation coefficient in the orthogonal coordinate system into the distribution of the linear attenuation coefficient in the projection coordinate system (so-called radon conversion). The orthogonal coordinate system is a coordinate system in which the subject 3 is fixed. The projected coordinate system is a coordinate system that represents the position when the X-ray generator 102 and the data collection device 106 are rotated by θ with respect to the orthogonal coordinate system.

  Next, the image reconstruction device 221 acquires the irradiation dose image 6 created in S103 of FIG. 3 (S204), forward-projects the irradiation dose image 6, and converts it into irradiation dose projection data 51 (S205). ). The forward projection process in S205 is the same as the forward projection process in S203.

  Next, an exposure dose image that is an image showing the distribution of the exposure dose of the subject is created using the reconstructed image and the irradiation X-ray image corresponding to the creation area of the reconstructed image. In other words, the image reconstruction device 221 performs reverse attenuation correction processing on the irradiation dose projection data 51 using the attenuation coefficient projection data 50 (S206). Specifically, the image reconstruction device 221 generates attenuation correction irradiation dose projection data 52 according to the following equation (1).

g_E(X,θ)：減弱補正照射線量投影データ
g_T(X,θ)：減弱係数投影データ
g₀(X,θ)：照射線量投影データ
通常の減弱補正は、補正対象データ(通常は、被検者3を透過したX線の線量を示すデータ)に対して減弱分を元に戻す作用がある。一方、S206の処理は、補正対象データ(S206では、被検者3に照射したX線の線量を示すデータ)に対して減弱分を削減する作用がある為、「逆」減弱補正と呼ぶことにする。

g _E (X, θ): attenuation correction irradiation dose projection data
g _T (X, θ): attenuation coefficient projection data
g ₀ (X, θ): Irradiation dose projection data Normal attenuation correction is a function that restores the attenuation to the correction target data (usually data indicating the X-ray dose transmitted through the subject 3). There is. On the other hand, the process of S206 has the effect of reducing attenuation with respect to the correction target data (data indicating the X-ray dose irradiated to the subject 3 in S206), so it is called “reverse” attenuation correction. To.

  In the reverse attenuation correction process of S206, correction may be added in consideration of the influence of X-ray scattering, refraction, and diffraction by the subject 3 and X-ray directivity.

  Next, the image reconstruction device 221 performs back projection processing on the attenuation correction irradiation dose projection data 52 to create an irradiation dose correction image 8 (S207). Here, the back projection process is a process of converting the distribution of the linear attenuation coefficient in the projection coordinate system into the distribution of the linear attenuation coefficient in the orthogonal coordinate system (so-called inverse radon conversion).

  The irradiation dose correction image 8 includes essential information for evaluating the exposure of the subject 3. S208 and S209, which will be described later, are processes for converting the irradiation dose correction image 8 into existing dose units.

  Next, the image reconstruction device 221 obtains a difference between the irradiation dose correction image 8 from the irradiation dose image 6 and creates an absorbed dose image based on the obtained difference (S208). The difference between the irradiation dose image 6 and the irradiation dose correction image 8 indicates the amount of attenuation by the subject 3. In the present invention, it is assumed that the attenuation amount by the subject 3 corresponds to the absorbed dose of the subject 3. The absorbed dose image is an image having a distribution similar to the irradiation dose image 6.

  Next, the image reconstruction device 221 creates an equivalent dose image by multiplying the absorbed dose image by the radiation load coefficient (S209). As defined above, the ICRP recommendation is that the radiation weighting factor in photons is 1, not limited to the energy range, so the absorbed dose image and the equivalent dose image are the same.

Next, the image reconstruction device 221 performs region determination based on the CT value of the tomographic image 5, identifies a region such as an organ, and creates an organ discrimination image (S210). The organ discrimination image is a map of an organ or the like, for example, a label image with a different label for each organ or the like.
Note that the region determination may be performed based on characteristics of an anatomical shape such as an organ instead of the CT value.

  Further, the image reconstruction device 221 may not only identify a region such as an organ but also identify a part of a human body and create a part-specific image.

  Next, the image reconstruction device 221 creates a tissue load coefficient image using a tissue load coefficient corresponding to an organ or the like (S211). As the tissue load coefficient, for example, the value shown in the recommendation of ICRP can be used.

  The image reconstruction unit calculates the exposure dose. That is, the image reconstruction device 221 collates the organ discrimination image and the equivalent dose image (or absorbed dose image), and creates a tissue load coefficient image. The tissue load coefficient image shows the calculation result of the exposure dose for each organ or the like. With the tissue load coefficient image, it becomes possible to evaluate the exposure dose for each organ or the like of the subject 3.

  Further, the image reconstruction device 221 may collate the region-specific image with the equivalent dose image (or absorbed dose image) to create a region load coefficient image. The part load coefficient image shows the calculation result of the exposure dose for each part of the human body (head, chest, abdomen, limbs, etc.).

  Next, the image reconstruction device 221 converts the equivalent dose image into an effective dose image using the tissue load coefficient image, and sets the effective dose image as the exposure dose image (S212). As described above, the effective dose image is an image obtained by weighting the tissue load coefficient with respect to the equivalent dose image.

Further, the image reconstruction device 221 may convert the absorbed dose image into an exposure dose image using a dose equivalent conversion coefficient. As the dose equivalent conversion factor, for example, the value shown in the recommendation of ICRP can be used.
Returning to the description of FIG. Next, the display device 211 of the X-ray CT apparatus displays dose information (S105).

Hereinafter, a display example of dose information will be described with reference to FIG.
The display device 211 displays a dose management screen 700 as shown in FIG. 7 based on the calculation result of the image reconstruction device 221.

  The dose management screen 700 shown in FIG. 7 includes a coronal image exposure image 9a, an axial image exposure image 9b, an irradiation range image 701 in which the irradiation image 6 is superimposed on the virtual image 3a of the subject 3, Includes exposure dose 702, exposure dose index conversion button 703, exposure dose by imaging 704, exposure dose by region 705, exposure dose by organ 706, exposure dose 707 within the ROI (region of interest), and ON / OFF button 708 for image display It is.

  When the on-image display is turned on by the on-image display ON / OFF button 708, the exposure dose images 9a and 9b include partial information on the region-specific dose 705, organ-specific dose 706, and ROI internal dose 707. Is displayed.

  In the exposure dose image 9a, the lung exposure dose 706a, the ROI 707a, and the ROI exposure dose 707b are superimposed and displayed. In the exposure dose image 9b, an abdominal exposure dose 705a, a liver exposure dose 706b, and a spine exposure dose 706c are superimposed and displayed.

  In the irradiation range image 701, in addition to the virtual image 3a of the subject 3 and the irradiation dose image 6, a cylindrical three-dimensional irradiation dose data 2000 and a circular region 4b indicating a cut-out plane of the irradiation dose image 6 are displayed. Has been.

  The irradiation range image 701 allows the user to roughly grasp the X-ray irradiation range for the subject 3.

  The exposure dose by imaging 702 displays the exposure dose by tomography, the exposure dose by simple imaging (scanogram imaging), and the cumulative exposure dose by tomography and simple imaging. The calculation of the exposure dose by simple imaging and the cumulative exposure dose by tomographic imaging and simple imaging will be described in an embodiment described later.

  An exposure dose index conversion button 703 is a button for converting an exposure dose index into another index. Other indices include existing indices such as CTDI (Computed Tomography Dose Index), DLP (Dse Length Product), CTDIw (weighted CTDI), CTDIvol (volumetric CTDI), and user-defined indices. The image reconstruction device 221 calculates CTDI, DLP, CTDIw, and CTDIvol based on the irradiation dose image 6.

  In the irradiation dose 704 for each imaging, an irradiation dose by rotating imaging (corresponding to tomographic imaging), an irradiation dose by still imaging (corresponding to scanogram imaging), and a cumulative irradiation dose by rotating imaging and stationary imaging are displayed. In addition, calculation of the exposure dose by still photography and the cumulative irradiation dose by rotation photography and still photography will be described in an embodiment described later.

The site-specific exposure dose 705 displays the exposure dose of the head, chest, abdomen, and extremities.
The organ-specific exposure dose 706 displays the exposure dose of bone, brain, lung, stomach, intestine, liver, breast, bladder and the like.
In the ROI exposure dose 707, the exposure dose in the ROI is displayed.

  As described above, according to the first embodiment, in tomographic imaging (rotational imaging), it is possible to quickly evaluate the exposure dose of the subject 3 and the irradiation dose to the subject 3 according to the imaging conditions.

  Furthermore, the exposure dose of the subject 3 and the irradiation dose to the subject 3 can be evaluated and managed in high speed, high accuracy and in detail.

  In the present invention, since the physical characteristics reflecting the morphological information included in the reconstructed image (clinical image information) and the substance configuration of the subject 3 are used, those different from human tissues such as indwelling materials and contrast agents, and irradiation X Applicable to CT tomographic images where there is a subject that significantly attenuates the line as subject 3 or a radiography method that modulates the intensity and energy of irradiated X-rays at short time intervals during radiography. Yes, the exposure dose of the subject can be evaluated.

  In addition, since only the morphological information and physical characteristics are referenced from the reconstructed image, the exposure dose can be evaluated even for reconstructed images that have undergone image reconstruction methods or image processing methods that change the image characteristics. it can.

  In addition, because it is possible to provide irradiation dose images, it is also possible to evaluate and manage irradiation doses, and easily convert them into indicators of exposure dose specific to existing CT examinations (CTDI, DLP, CTDIw, CTDIvol, etc.) can do.

  In particular, the three-dimensional distribution of the irradiation X-ray dose is considered for each pixel in the image for evaluating the exposure dose by the processing shown in S201 to S207 shown in FIG. Since the attenuation amount in consideration of the shape of the person 3 can be calculated, the exposure dose of the subject 3 can be evaluated with high accuracy.

  In addition, in the processes shown in S201 to S207 shown in FIG. 5, the calculation process for each organ or the like of the subject 3 (for example, the process for calculating the X-ray transmission length for each organ or the like) is not performed. Even if there are many organs or the like in the image for evaluating the dose, the calculation amount is small, and the calculation time can be shortened.

  Further, by S210 to S211 shown in FIG. 5, the exposure dose can be calculated for each organ or the like by using the value indicated in the ICRP recommendation. This is because the absorbed dose can be calculated with high accuracy in units of pixels by the processing shown in S201 to S207 shown in FIG.

[Second Embodiment]
In the first embodiment, the evaluation of the exposure dose by tomography (rotation imaging) has been described. In the second embodiment, the evaluation of the exposure dose by scanogram imaging (still imaging) will be described.

  Scanogram imaging is still imaging and is imaging for obtaining a scanogram image of a subject 3 (a moving image in which movement of an organ or the like of the subject 3 can be confirmed).

The processing of the X-ray CT apparatus in the second embodiment will be described with reference to FIGS.
The subject 3 image in the second embodiment is the scanogram image 10 of the subject 3 shown in FIG. The area 4c in the imaging range of the scanogram image 10 is an area parallel to the YZ plane. The scanogram image 10 may be either a single image or a plurality of images, and is not particularly limited. Further, the scanogram image 10 may be taken from the front, the plane, the left side, the right side, or any other direction of the subject 3, or may be taken multiple times by combining a plurality of directions. You may do it.

  As shown in FIG. 9, the image reconstruction device 221 of the X-ray CT apparatus acquires the scanogram image 10 shown in FIG. 4 (S301), and converts the scanogram image 10 to the attenuation ratio image 11 based on the attenuation reference value. (S302).

  The attenuation ratio image 11 is an image showing the distribution of the attenuation ratio. The attenuation ratio is a value (relative value) indicating the ratio of each pixel value with reference to the attenuation reference value.

  The attenuation reference value may be data measured in advance, data obtained by numerical simulation, or an average pixel value of a partial region 12 (see FIG. 10) of the scanogram image. The partial area 12 of the scanogram image is preferably an air area, but may be an area of a substance other than that.

  Next, the image reconstruction device 221 acquires irradiation X-ray information from the storage device 213 according to the imaging conditions. The image reconstruction device 221 performs irradiation X-rays at each time (t = t0,..., Tn) at predetermined time intervals from the start of X-ray irradiation (t = t0) to the end of irradiation (t = tn). Information is acquired from the storage device 213.

  The irradiation X-ray information is the three-dimensional irradiation intensity distribution data 1101 shown in FIG. In the example shown in FIG. 8, the three-dimensional irradiation intensity distribution data 1101 includes the X-ray beam spread (fan angle) in the slice plane direction (xy plane direction) and the X-ray beam in the body axis direction (z axis direction). Of spread (cone angle). However, the three-dimensional irradiation intensity distribution data 1101 is not limited to the example shown in FIG.

  Next, the image reconstruction device 221 time-integrates a set 1100 of 3D irradiation intensity distribution data at each time, and performs a projective transformation from 3D to 2D according to the scanogram image 10 (in the example shown in FIG. 8). For example, two-dimensional irradiation dose data 2100 is created by performing projection conversion to the yz plane. Then, the image reconstruction device 221 creates an irradiation dose image 6 (stationary imaging irradiation dose image, irradiation X-ray image) having the same region 4d as the imaging region 4c of the scanogram image 10 (S303).

  Next, the image reconstruction device 221 calculates the attenuation amount by the subject 3 by performing reverse attenuation correction processing on the irradiation dose image 6 using the attenuation ratio image 11 (S304), and the subject 3 Assuming that the attenuation amount corresponds to the amount absorbed by the subject 3, an absorbed dose image 16 (stationary imaging absorbed dose image) is created (S305).

  Since the second embodiment is still shooting, forward projection processing and backprojection processing are not performed. That is, processing corresponding to the projection data generation processing (S203, S205) and the irradiation dose correction image generation processing (S207) in the first embodiment is not performed.

  In the reverse attenuation correction process in S304, the image reconstruction device 221 creates an absorbed dose image according to the following equation (2).

fA：吸収線量画像 f0：照射線量画像
fT：減弱比画像 ft：スキャノグラム画像
k：減弱基準値
次に、画像再構成装置221は、線量当量換算係数を用いて、吸収線量画像16を被曝線量画像に変換する(S306)。線量当量換算係数は、例えば、ICRPの勧告に示される値を用いることができる。

fA: Absorption dose image f0: Irradiation dose image
fT: attenuation ratio image ft: scanogram image
k: Attenuation Reference Value Next, the image reconstruction device 221 converts the absorbed dose image 16 into an exposure dose image using a dose equivalent conversion coefficient (S306). As the dose equivalent conversion factor, for example, the value shown in the recommendation of ICRP can be used.

As in the first embodiment, the display device 211 of the X-ray CT apparatus displays dose information.
As described above, according to the second embodiment, in scanogram imaging (still imaging), it is possible to quickly evaluate the exposure dose of the subject 3 and the irradiation dose to the subject 3 according to the imaging conditions.
Furthermore, the exposure dose of the subject 3 and the irradiation dose to the subject 3 can be evaluated and managed with high accuracy and detail. In addition, since scanogram imaging is still imaging, exposure dose and irradiation dose can be evaluated and managed in the same manner as scanogram imaging.

  In the present invention, because the physical information reflecting the morphological information included in the subject image (clinical image information) and the substance configuration of the subject 3 is used, it is different from the human tissue such as an indwelling object or a contrast agent or irradiation. Even if there is something that significantly attenuates X-rays as the subject 3, the exposure dose can be evaluated.

  In addition, because it is possible to provide an irradiation dose image that shows the distribution of the X-ray irradiation dose irradiated to the subject 3, it is also possible to evaluate and manage the irradiation dose, which is unique to existing CT examinations. Can be easily converted to other indices (CTDI, DLP, CTDIw, CTDIvol, etc.).

  In addition, in the processes shown in S301 to S305 shown in FIG. 9, the calculation process for each organ of the subject 3 (for example, the process for calculating the X-ray transmission length for each organ, etc.) is not performed. Even if there are many organs or the like in the image for evaluating the dose, the calculation amount is small, and the calculation time can be shortened.

[Third embodiment]
In the first embodiment and the second embodiment, the evaluation of each exposure dose has been described for tomographic imaging (rotational imaging) and scanogram imaging (static imaging), but in the third embodiment, the tomographic imaging is performed. A case will be described where both shooting (rotation shooting) and scanogram shooting (still shooting) are performed, and there are overlapping areas in the shooting range.

Processing of the X-ray CT apparatus in the third embodiment will be described with reference to FIG.
The X-ray CT apparatus performs scanogram imaging and tomographic imaging based on the set imaging conditions, and acquires a scanogram image and a tomographic image.

  Next, the image reconstruction device 221 of the X-ray CT apparatus acquires irradiation X-ray information in scanogram imaging from the storage device 213 according to the imaging conditions. The image reconstruction device 221 is used at each time (t = ts0,..., Tsn) at predetermined time intervals from the start of X-ray irradiation (t = ts0) to the end of irradiation (t = tsn) in scanogram imaging. Irradiation X-ray information is acquired from the storage device 213. The irradiation X-ray information in the scanogram imaging is a set 1100 of three-dimensional irradiation intensity distribution data shown in FIG.

  Further, the image reconstruction device 221 acquires irradiation X-ray information in tomography from the storage device 213 according to the imaging conditions. The image reconstructing apparatus 221 is configured at each time (t = tr0,..., Trn) at predetermined time intervals from the start of X-ray irradiation (t = tr0) to the end of irradiation (t = trn) in tomography. Irradiation X-ray information is acquired from the storage device 213. The irradiation X-ray information in tomography is a set 1000 of three-dimensional irradiation intensity distribution data shown in FIG.

  Next, the image reconstruction device 221 synthesizes both a set 1100 of 3D irradiation intensity distribution data in scanogram imaging and a set 1000 of 3D irradiation intensity distribution data in tomography at each time, and combines the combined 3D Cumulative three-dimensional irradiation dose data 2200 is created by time integration of a set 1200 of irradiation intensity distribution data.

  Next, the image reconstruction device 221 extracts the pixel value of the accumulated 3D irradiation data 2200 in the cutout plane, using the area 4e at the same z position as the area indicating the tomographic plane of the evaluation tomographic image as the cutout plane. Thus, the cumulative irradiation dose image 15 is obtained.

  In addition, the cumulative irradiation dose image 15 shown in FIG. 11 is expressed with a constant pixel value, but actually has a different pixel value for each pixel. That is, the cumulative irradiation dose image 15 is an image having a distribution.

Next, as in the first embodiment, the image reconstruction device 221 creates a cumulative exposure dose image using the tomographic image to be evaluated and the cumulative irradiation dose image 15.
Then, the display device 211 of the X-ray CT apparatus displays dose information as in the first embodiment.

  As described above, according to the third embodiment, both tomographic imaging (rotational imaging) and scanogram imaging (still imaging) are performed, and when there are overlapping areas in the imaging range, the subject according to the imaging conditions The cumulative exposure dose of 3 and the cumulative exposure dose to the subject 3 can be quickly evaluated.

  Furthermore, the accumulated dose of the subject 3 and the accumulated dose to the subject 3 can be evaluated and managed with high accuracy and detail.

[Fourth embodiment]
In the third embodiment, 3D irradiation intensity distribution data in scanogram imaging and 3D irradiation intensity distribution data in tomography are synthesized, and the cumulative exposure dose and the cumulative irradiation dose are evaluated. In the embodiment, synthesizing an exposure dose image will be described.

Processing of the X-ray CT apparatus in the fourth embodiment will be described with reference to FIG.
The X-ray CT apparatus performs scanogram imaging and tomographic imaging based on the set imaging conditions, and acquires a scanogram image and a tomographic image.

  Next, the image reconstruction device 221 of the X-ray CT apparatus creates the tomographic exposure dose image 9c as described in the first embodiment. FIG. 12 shows tomographic exposure dose images 9c at a plurality of slice positions (z positions).

  Next, as described in the second embodiment, the image reconstruction device 221 creates a scanogram imaging exposure dose image 9d. The scanogram imaging exposure dose image 9d shown in FIG. 12 is an image showing the exposure dose of the scanogram imaging captured from the front direction of the subject 3.

  Next, the image reconstruction device 221 projects the tomographic exposure dose image 9c in the scanning direction of scanogram imaging, and generates the exposure dose data 13 per unit thickness (thickness means slice thickness). In the graph of the exposure dose data 13 shown in FIG. 12, the horizontal axis indicates the position in the body width direction (x direction) of the subject 3, and the vertical axis indicates the exposure dose per unit thickness.

Next, the image reconstruction device 221 adds each exposure dose data 13 to the corresponding slice position 14 of the scanogram imaging exposure dose image 9d to create a cumulative exposure dose image.
Then, the display device 211 of the X-ray CT apparatus displays dose information as in the first embodiment.

As described above, according to the fourth embodiment, it is possible to synthesize a plurality of exposure dose images and quickly evaluate the cumulative exposure dose of the subject 3 according to the imaging conditions.
Furthermore, the accumulated dose of the subject 3 can be evaluated and managed with high accuracy and detail.

  In the first to fourth embodiments described above, the image reconstruction device 221 of the X-ray CT apparatus creates an irradiation dose image, an exposure dose image, and the like, but the present invention is not limited to this.

For example, instead of the image reconstruction device 221, a CPU (control unit) of a computer (medical image processing device) that performs medical image processing may create an irradiation dose image, an exposure dose image, or the like. In this case, the medical image processing apparatus acquires from the X-ray CT apparatus imaging conditions, information that is the basis of the reconstructed image of the subject, and the like. For example, the X-ray CT apparatus may transmit such information to the medical image processing apparatus via a network. Further, for example, the X-ray CT apparatus may store these information in a storage medium, and the medical image processing apparatus may read out the information from the storage medium.

  In this case, the medical image processing apparatus stores three-dimensional irradiation intensity distribution data (irradiation X-ray information) in a storage device (storage unit) for each imaging condition.

Then, the control unit of the medical image processing apparatus acquires irradiation X-ray information from the storage unit according to the imaging conditions, and creates a dose image based on the irradiation X-ray information and the reconstructed image of the subject. To do. The display device (display unit) of the medical image processing apparatus displays dose information such as an exposure dose image.

  The preferred embodiments of the X-ray CT apparatus and the like according to the present invention have been described above with reference to the accompanying drawings, but the present invention is not limited to such examples. It will be apparent to those skilled in the art that various changes or modifications can be conceived within the scope of the technical idea disclosed in the present application, and these naturally belong to the technical scope of the present invention. Understood.

1 Imaging means, 2 Operating means, 3 Subject, 4a, 4b, 4c, 4d, 4e area, 5 Tomographic image, 6 Irradiation dose image, 7 Attenuation coefficient image, 8 Irradiation dose correction image, 9a Coronal image exposure dose Image, 9b Axial exposure image, 9c Tomographic exposure image, 9d Scanogram exposure image, 10 Scanogram image, 11 Attenuation ratio image, 12 Partial region of scanogram image, 13 Exposure data, 14 Slice position , 15 Cumulative dose image, 16 Absorbed dose image, 50 Attenuation coefficient projection data, 51 Irradiation dose projection data
52 Attenuation-corrected irradiation dose projection data, 100 gantry, 101 bed apparatus, 102 X-ray generator, 103 X-ray detector, 104 collimator, 105 high voltage generator, 106 data collector, 107 drive, 200 central controller , 201 I / O device, 202 Arithmetic unit, 211 Display device, 212 Input device, 213 Storage device, 221 Image reconstruction device, 222 Image processing device, 700 Dose management screen, 701 Irradiation range image, 702 Exposure dose by imaging, 703 Dose index conversion button, 704 Radiation exposure by imaging, 705 Exposure dose by region, 705a Abdominal exposure dose, 706 Organ exposure dose, 706a Lung exposure dose, 706b Liver exposure dose, 706c Spine exposure dose, 707a ROI , 707b ROI exposure dose, 707 ROI exposure dose, 708 ON / OFF button for image display, 1000, 1100 3D irradiation intensity distribution data set, 1001, 1101 3D irradiation intensity distribution data, 1200 Synthesized 3 Set of two-dimensional irradiation intensity distribution data, 20 00 3D irradiation data, 2100 2D irradiation data, 2200 Cumulative 3D irradiation data

Claims (11)

An X-ray irradiation unit that emits X-rays from around the subject; and
An X-ray detector that detects X-rays transmitted through the subject as X-ray information;
A reconstructed image of a subject is created from the X-ray information, and irradiation X is a distribution of irradiation intensity of X-rays irradiated to the subject by the X-ray irradiation unit according to imaging conditions. Get line images,
By converting the CT value of the reconstructed image into an attenuation coefficient based on the information indicating the relationship between the CT value and the attenuation coefficient, an attenuation coefficient image that is an image showing the distribution of the attenuation coefficient is created,
Projection data of the attenuation coefficient image is obtained by performing forward projection processing, which is conversion from an orthogonal coordinate system to a projection coordinate system, on the attenuation coefficient image and the irradiation dose image created using the irradiation X-ray image. And projection data of the irradiation dose image is generated, reverse attenuation correction processing is performed on the projection data of the irradiation dose image using the projection data of the attenuation coefficient image, and the irradiation dose image after the reverse attenuation correction processing is processed. By performing a back projection process that is a transformation from the projection coordinate system to the orthogonal coordinate system on the projection data, an irradiation dose correction image that is an image showing the reduction result of the attenuation amount with respect to the irradiation dose image is created,
Absorption, which is an image showing the distribution of the X-ray dose absorbed by the subject based on the difference between the irradiation dose image and the irradiation dose correction image, which is an image showing the attenuation reduction result with respect to the irradiation dose image Create a dose image,
By identifying the region of the organ and / or tissue in the reconstructed image and collating with the absorbed dose image , the dose distribution of the subject can be calculated by calculating the dose for each organ and / or tissue. and images reconstruction unit to create a radiation dose image is an image showing,
An X-ray CT apparatus comprising: the exposure dose image and a display unit that displays the exposure dose.   2. The X-ray CT apparatus according to claim 1, wherein the image reconstruction unit creates an accumulated dose image that is an image showing a distribution of the accumulated dose of the subject based on the plurality of dose images.   The image reconstruction unit generates irradiation dose data by integrating the irradiation X-ray image at each time for each predetermined time interval from irradiation start to irradiation end, and based on the irradiation dose data, 2. The X-ray CT apparatus according to claim 1, which creates an irradiation dose image that is an image showing a distribution of an X-ray dose irradiated to a subject. 4. The X-ray CT apparatus according to claim 3 , wherein the display unit displays the irradiation dose image superimposed on a virtual image of a subject. The image reconstruction unit integrates time of the irradiation X-ray image related to rotation imaging and stationary imaging of the irradiation X-ray image, so that the X-ray dose irradiated to the subject in the rotation imaging and still imaging is calculated. 4. The X-ray CT apparatus according to claim 3 , wherein a cumulative irradiation dose image that is an image showing a distribution is created. The image reconstruction unit is an image showing the distribution of the dose of X-rays irradiated to the subject in stationary imaging by time-integrating the irradiated X-ray image related to still imaging of the irradiated X-ray image. 4. The X-ray CT apparatus according to claim 3 , which creates a static imaging irradiation dose image. The image reconstruction unit creates an attenuation ratio image that is an image showing an attenuation ratio distribution from a still photographed image based on information indicating an attenuation reference value,
A static radiography absorption dose image, which is an image showing a distribution of X-ray dose absorbed by the subject in static imaging by performing reverse attenuation correction processing on the static radiography irradiation dose image using the attenuation ratio image 7. The X-ray CT apparatus according to claim 6 , wherein the X-ray CT apparatus is created. 4. The X-ray CT apparatus according to claim 3 , wherein the image reconstruction unit calculates one of CTDI, DLP, CTDIw, or CTDIvol based on the irradiation dose image. 2. The X-ray CT apparatus according to claim 1 , wherein the display unit displays an exposure dose for each organ and / or tissue. 2. The X-ray CT apparatus according to claim 1 , wherein the image reconstruction unit calculates an exposure dose for each region by identifying a region of each region in the reconstructed image and comparing the region with the absorbed dose image. 11. The X-ray CT apparatus according to claim 10 , wherein the display unit displays an exposure dose for each part.

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